1. Field of the Invention
The present invention relates generally to optical fibers, and particularly to optical fibers with low attenuation and low Small Angle Scattering (SAS) loss.
2. Technical Background
Telecommunication systems, for the underground and undersea applications in particular, require optical fiber which is capable of transmitting signals for a long distance without degradation. The appearance of new technologies, such as wavelength division multiplexing (WDM) and high channel speed, makes possible to satisfy the ever-growing demand for network bandwidth. However, the optical fiber attributes such as attenuation and bend loss contribute to the degradation of the signal.
US patent publication 2003/0161597 discloses an optical fiber capable of multi mode operation at wavelengths below 1300 nm and single mode operation at wavelengths above 1300 nm. The publication describes that this optical fiber has reduced intermodal noise, but is silent with regard to overall attenuation and Small Angle Scattering (SAS) loss.
The article by Rawson E. G., entitled “Measurement of the Angular Distribution of Light Scattered from a Glass Fiber Optical Waveguide”, App. Opt. 11, 2477 (1972) describes the measurement of angular distribution of a near-forward scattering, and proposes that it is caused by narrow dielectric needles aligned with the fiber axis.
The article by Rawson E. G., entitled “Analysis of Scattering from Fiber Waveguide with Irregular Core Surfaces”, App. Opt. 13, 2370 (1974) describes an induced-dipole scattering method and presents the results of the angular distribution of scattering for five types of perturbations on the core-cladding interface of the optical fiber.
The article by Lines, M. E., Reed W. A., Di Giovanni D. J. and Hamblin J. R., entitled “Explanation of Anomalous Loss in High Delta Single mode Fibers”, Ele. Lett., 35, 1009 (1999) describes the angular dependence of anomalous scattering is caused by fluctuation of refractive index of the material along axial and azimuthal directions. The loss is predicted to be related the fiber profile peak and profile shape.